1. Field of the Invention
The present invention generally relates to a gas exhaust system for removing extraneous gasses, resultant by-product gasses or the like from a process chamber of a semiconductor manufacturing device such as a CVD apparatus. In particular, the present invention pertains to a gas exhaust system for use in a semiconductor manufacturing process, which is capable of preventing oil leakage from a vacuum pump provided therein to the side of a process chamber of a semiconductor manufacturing device in which wafers or substrates to be processed are arranged, and which is capable of maintaining the vacuum pump of the gas exhaust system to be an optimum operational state.
2. Related Art Description
There have been known a variety of semi conductor manufacturing devices such as a CVD device. The CVD device, for example, has an air-tight process chamber in which a plurality of silicon wafers or the like to be processed are arranged. After the wafers are processed in the chamber, residual gasses, resulting by-product gasses must be removed from the process chamber of the device. For this purpose, a gas exhaust system is provided to the semiconductor manufacturing devices.
One such conventional gas exhaust systems has an oil rotary vacuum pump. This type of pump has a cylinder arranged in oil stored in a casing thereof and eccentric rotors rotatably arranged in the cylinder. The rotors are rotated in the cylinder in a condition that sealing is formed between the vanes of the rotors and the inner surface of the cylinder, so that a certain degree of vacuum state is formed in the cylinder, and therefore, the gases remaining in the process chamber of the semiconductor manufacturing device can be exhausted via the pump.
However, in this system, the sealing oil in the pump may leak or diffuse therefrom and flows into the process chamber of the device to deposit on the surface of the chamber. If a large amount of sealing oil is leaked into the process chamber of the device, it cannot be expected to perform an appropriate processing of the silicon wafers arranged in the chamber. In addition, it may fall into a condition that an oil-free state on an order of 10.sup.-3 Tort cannot be created in the chamber.
Another typical gas exhaust system associated with the semiconductor manufacturing devices is one that has a root-type multi-stage pump. The root-type pump has a pair of rotors of a cocoon shape which are arranged in a cylinder having an elliptic section in a manner that they are offset by 90 degrees with respect to each other. By rotation of the rotors, gas exhaust operation is carried out. Typically, a plurality of this type of pumps are connected serially to form a root-type multi-stage pump system.
In this system, the gasses exhausted from the process chamber of the semiconductor manufacturing device are sometimes excessively or unneccessary compressed in the pump. Thus, the exhausted gasses are condensed and solidified in the pump, which causes clogging of the rotors of the pump and to undesirably stop the operation of the pump. When the rotors fall in a clogged condition, the pump itself must be removed from the gas exhaust line of the semiconductor manufacturing device so that it is disassembled and is washed to remove the deposits therein. This kind of recovery operation of the pump takes much time, usually at least several days, and during this recovery operation, the semiconductor manufacturing line must be stopped. This reduces the productivity of the manufacturing line. Further, it is observed that the lubricant oil of the pump leaks into the process chamber of the semiconductor manufacturing device, although the amount of which is not so much as that occurred in the above-mentioned oil vacuum pump.